This invention relates to ink jet printing devices and more particularly to a thermal ink jet printhead having an array of coplanar nozzles in a nozzle face that are entirely surrounded by an insulative polymeric material, together with a method of fabrication thereof.
Thermal ink jet printing is a type of drop-on-demand ink jet systems wherein an ink jet printhead expels ink droplets on demand by the selective application of a current pulse to a thermal energy generator, usually a resistor, located in capillary-filled parallel ink channels a predetermined distance upstream from the channel nozzles or orifices. The channels ends opposite the nozzles are in communication with an ink reservoir to which an external ink supply is connected. The current pulses momentarily vaporize the ink and form bubbles on demand. Each temporary bubble expels an ink droplet and propels it towards a recording medium. The printing system may be incorporated in either a carriage-type printer or pagewidth type printer. A carriage-type printer generally has a relatively small printhead containing the ink channels and nozzles. The printhead is usually sealingly attached to a disposable ink supply cartridge in a combined printhead and cartridge assembly which is reciprocated to print one swath of information at a time on a stationarily held recording medium, such as paper. After the swath is printed, the paper is stepped a distance equal to the height of the printed swath so that the next printed swath will be contiguous therewith. The procedure is repeated until the entire page is printed. In contrast, the pagewidth printer has a stationary printhead having a length equal to or greater than the width of the paper. The paper is continually moved past the printhead in a direction normal to the printhead length and at a constant speed during the printing process.
U.S. Pat. No. Re. 32,572 to Hawkins et al discloses a thermal ink jet printhead and method of fabrication. In this case, a plurality of printheads may be concurrently fabricated by forming a plurality of sets of heating elements with their individual addressing electrodes on one substrate, generally a silicon wafer, and etching corresponding sets of channel grooves with a common recess for each set of grooves in another silicon wafer. The wafer and substrate are aligned and bonded together so that each channel has a heating element. The individual printheads are obtained by milling away the unwanted silicon material to expose the addressing electrode terminals and then dicing the substrate to form separate printheads.
U.S. Pat. No. 4,638,337 to Torpey et al discloses an improved printhead of the type disclosed in the patent to Hawkins et al wherein the bubble generating resistors are located in recesses to prevent lateral movement of the bubbles through the nozzles and thus preventing sudden release of vaporized ink to the atmosphere that would result in ingestion of air.
U.S. Pat. No. 4,567,493 to Ikeda et al discloses a liquid jet recording head, including a plurality of protection layers, one of which has a region that directly contacts liquid. A principle function of the protection layer is to prevent penetration by the liquid and therefore prevent a failure mode for the bubble generating resistors and their addressing electrodes. It further discloses a liquid jet recording head wherein a liquid flow path is formed in the recording head by laminating a photosensitive resin dry film onto a base. The resin is photopatterned to form the liquid flow path and a liquid reservoir. A glass substrate is then adhesively bonded to the base to form the recording head.
U.S. Pat. No. 4,786,357 to Campanelli et al discloses the use of a patterned thick film insulative layer between mated and bonded substrates. One substrate has a plurality of heating element arrays and addressing electrodes formed on the surface thereof and the other being a silicon wafer having a plurality of etched reservoirs with each reservoir having a set of ink channels. The patterned thick film layer provides a clearance space above each set of contact pads of the addressing electrodes to enable the removal of the unwanted silicon material by dicing without the need for etched recesses therein. The individual printheads are produced subsequently by dicing the substrate having the heating element arrays.
U.S. Pat. No. 4,774,530 to Hawkins discloses the use of an etched thick film insulative layer to provide the flow path between the ink channels and the reservoir, thereby eliminating the fabrication steps required to open the channel groove closed ends to the manifold recess so that the printhead fabrication process is simplified.
A major problem with the existing ink jet printing devices is directionality of the ejected ink droplets. Any ridge or chip at the nozzle, any dried ink around the nozzle, or any different materials surrounding the nozzles which vary in wettability will have an effect on the droplet directionality. This invention solves the directionality problem by providing a nozzle that is entirely surrounded by the same material which provides a uniformly wettable surface and by greatly reducing the geometric effects such as ink formation or ridges or chips in the vicinity of the nozzle.